1. Field of the Invention
The present invention relates to an integrated circuit device with a built-in monolithic temperature sensor, a method of manufacturing the device, and a method of forming a vanadium oxide film, and, more particularly, to an integrated circuit device using a resistor film of vanadium oxide for a temperature sensor, a method of manufacturing the device, and a method of forming a vanadium oxide film.
2. Description of the Related Art
Recently, there are growing needs for monitoring the operation temperature of an integrated circuit device. The purpose of monitoring the operation temperature is preventing thermal breakdown of elements in the integrated circuit device and stabilizing the operation of elements whose characteristic has temperature dependence.
In this respect, Japanese Patent Laid-Open Publication No. H1-302849, for example, discloses a technique of providing a temperature sensor on the same substrate as that of an LSI (Large Scale Integrated circuit). In the technique, the temperature sensor decides that the LSI is abnormally overheated when the temperature detected by the temperature sensor exceeds a predetermined value and then shutting down the LSI. Therefore, it can protect the LSI from thermally broken by a temperature rise. A resistor of which electric resistance changes with the temperature is used as a temperature sensor.
It is preferable that a material whose electric resistivity has as large a temperature coefficient as possible should be used for such a resistor. The present inventors have developed a technique of forming a vanadium oxide film as a resistor having an electric resistivity whose temperature coefficient has a large absolute value, and has disclosed it in, for example, Japanese Patent Laid-Open Publication No. H11-330051.
To form a resistor for measuring the temperature, a vanadium oxide film should be processed into a desired pattern. A typical method of processing a film into a desired pattern is to etch the film using a resist pattern as a mask. FIGS. 1 and 2 are cross-sectional views showing a conventional method of forming a vanadium oxide film step by step.
As shown in FIG. 1, a film 19a of vanadium oxide (VOx) is formed on the entire surface of an insulating layer 17. Next, a resist film is formed on the film 19a, and is patterned by photolithography to thereby form a resist pattern 20. With the resist pattern 20 as a mask, the film 19a is locally etched out. As a result, the film 19a is patterned to form a vanadium oxide film 19 (see FIG. 2). Thereafter, the resist pattern 20 is removed by dissolving the resist pattern 20 into a stripping solution or performing oxygen plasma ashing.
The prior art however has the following problem. As shown in FIG. 2, when the resist pattern 20 (see FIG. 1) is removed, the vanadium oxide film 19 may be damaged, thus forming a damaged portion 21 on the entire top surface and entire side surface of the vanadium oxide film 19. This point will be discussed in detail. In removing the resist pattern 20 with a stripping solution, acidic or alkaline solution or a solution containing an organic solvent is used for the stripping solution. One example of commercially available stripping solutions containing an organic solvent is a chemical containing 50% by mass of DMSO (Dimethyl Sulfoxide), 1% by mass of ammonium fluoride and 30% by mass of water (H2O). However, vanadium oxide has such properties as to be easily dissolved in both an acidic solution and alkaline solution and to be exhausted and dissolvable in water. Even the use of any of an acidic solution, an alkaline solution and a solution containing an organic solvent used as a stripping solution damages the vanadium oxide film 19 of vanadium oxide. When the resist pattern 20 is removed by oxygen plasma ashing, vanadium oxide is overoxidized, increasing the electric resistivity, so that the performance as a temperature sensor is degraded.
The present inventors have developed a technique of overcoming the problem to some extent and disclosed the technique in Japanese Patent Laid-Open Publication No. H11-330051. FIG. 3 is a cross-sectional view illustrating a method of forming a vanadium oxide film described in Japanese Patent Laid-Open Publication No. H11-330051. As shown in FIG. 3, the film 19a of vanadium oxide is formed on the insulating layer 17 by a method similar to the one illustrated in FIG. 1. Next, a silicon oxide film is formed on the film 19a. Then, the resist pattern 20 is formed on the silicon oxide film, and the silicon oxide film is locally etched out using the resist pattern 20 as a mask, thereby forming a patterned silicon oxide film 22. Thereafter, the resist pattern 20 is removed by dissolving the resist pattern 20 into a stripping solution or performing oxygen plasma ashing. Then, using the patterned silicon oxide film 22 as a mask, the film 19a is locally etched out, thereby forming a vanadium oxide film.
Because that portion of the film 19a which remains to be a vanadium oxide film after patterning is covered with the silicon oxide film 22 at the time of removing the resist pattern 20, this technology can prevent damages to the portion by the stripping solution or the oxygen plasma ashing to some extent.
The prior art however has the following problem. FIG. 4 is a cross-sectional views showing the problem of the prior art described in Japanese Patent Laid-Open Publication No. H11-330051. As shown in FIG. 4, in removing the resist pattern 20 (see FIG. 3), that portion of the film 19a which remains to be a vanadium oxide film after patterning is covered with the silicon oxide film 22, so that the entire top surface of the vanadium oxide film 19 is prevented from being damaged as shown in FIG. 2. However, the top surface of that portion of the film 19a which is not covered with the silicon oxide film 22 is damaged, and the damaged portion penetrates a part of the portion covered with the silicon oxide film 22. Apparently, even the technology disclosed in Japanese Patent Laid-Open Publication No. H11-330051 cannot completely inhibit damages on the resistor film.